A known indexing device is, for example, a device (rotary table) mounted on a bed of a machine tool and being capable of indexing a table on which a workpiece is mounted. For example, a rotary table disclosed in Patent Document 1 includes a frame having a through hole at the center of the frame, and a rotary shaft inserted into the through hole and supported rotatably relative to the frame. A table surface, on which a workpiece is mounted, of the rotary table is integrally provided with the rotary shaft. A worm wheel is accommodated within the frame, the worm wheel being integral with the rotary table. A worm spindle is also accommodated within the worm wheel in a manner meshing with the worm wheel. The worm spindle is linked with an actuator such as a servomotor. When the servomotor is rotationally driven, the rotary table being integral with the rotary shaft rotates by a desired angle, thereby carrying out an indexing operation.
Meanwhile, the rotary table disclosed in Patent Document 1 includes a clamp mechanism (clamp sleeve) which holds an angle (position) of the rotary table after the indexing operation. In particular, the rotary table includes a cylinder segment extending in parallel to the through hole of the frame and integrally provided with the rotary table, and a clamp sleeve having a ring shape and provided in a space between the cylinder segment and the frame. The clamp sleeve has a through hole therein. Also, the clamp sleeve includes, at an outer periphery thereof, a cylindrical portion fitted around the cylinder segment of the rotary table, and a flange portion continuously provided with the cylindrical portion and functioning as an attachment portion to the frame. The clamp sleeve has an annular groove provided around the cylindrical portion and extending along the outer periphery, so that a pressure chamber is formed between the annular groove and the through hole of the frame accommodating the cylindrical portion.
A clamp sleeve of related art used for a rotary table will be described below with reference to FIG. 11 which shows a peripheral portion of the clamp sleeve in an enlarged manner.
At a rotary table 103, a cylinder segment 104 extending in parallel to a through hole 102 of a frame 101 is integrally provided with the rotary table 103 through a screw member (not shown), and a clamp sleeve 105 having a ring shape is arranged in a space between the cylinder segment 104 and the through hole 102 of the frame 101. The clamp sleeve 105 includes a cylindrical portion 106 fitted around the cylinder segment 104 of the rotary table 103, and a flange portion 107 continuously provided with the cylindrical portion 106, extending outward in a radial direction, and functioning as an attachment portion to the frame 101. The clamp sleeve 105 has a through hole (inner peripheral end 110) therein for the continuously provide cylindrical portion 106 and flange portion 107. The flange portion 107 of the clamp sleeve 105 is fixed to an attachment portion (not shown) of the frame 101 through a screw member 115, and thus attached to the frame 101.
The cylindrical portion 106 has an annular groove 108 recessed from outer peripheral ends 109a, 109a′, and extending around an outer periphery of the cylindrical portion 106. In particular, the annular groove 108 has a pair of inner end surfaces 109b, 109b′ extending inward in the radial direction of a rotary shaft (not shown) and being separated from each other, and a groove bottom surface 109c extending in parallel to the through hole (inner peripheral end 110). Arcuate rounded surfaces 109d, 109d′ continuously extend between the inner end surfaces 109b, 109b′ and the groove bottom surface 109c. The rounded surfaces 109d, 109d′ have a curvature radius of about several millimeters. A pressure chamber 112 is formed between the annular groove 108 thus provided and the through hole 102 of the frame 101 accommodating the cylindrical portion. Also, the annular groove 108 of the clamp sleeve 105, has a thin-wall section (linearly extending portion) 111 in a region q1 provided with the groove bottom surface 109c. The thin-wall section 111 has a thickness which allows the thin-wall section 111 to be deformable by supplying pressure fluid to the pressure chamber 112.
The through hole 102 has annular grooves (not shown) for accommodating seal members 113, 113′. The seal members 113, 113′ are inserted into the annular grooves to be non-movable relative to the through holes 102 and to be in contact with the outer peripheral ends 109a, 109a′ of the cylindrical portion. The seal members 113, 113′ hold an air-tight or liquid-tight state for the pressure chamber 112 formed by the annular groove 108 and the through hole 102 of the frame 101 accommodating the cylindrical portion. On the other hand, the frame 101 has a channel 114 communicating with a fluid supply source (not shown) and the pressure chamber 112. During a clamping operation, the thin-wall section 111 expands inward in the radial direction of the rotary shaft by pressure fluid, e.g., pressure air or pressure oil, supplied to the pressure chamber 112. The thin-wall section 111 presses the cylinder segment 104 of the rotary table 103. Hence, the rotary table 103 with the angle thereof previously positioned can be held in a non-rotatable manner relative to the frame 101.
As such a rotary table, a rotary table is disclosed in Patent Document 1, in which rotation of an electric motor is transmitted to a table through a worm mechanism included in the rotary table. Alternatively, a rotary table is developed, in which a direct-drive type motor, that is, a DD motor, is included therein. For example, the rotary table is disclosed in Japanese Patent Application No. 2005-319586 suggested by the applicant of the present invention.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-103181 (FIGS. 1, 3)